The Moon’s interior is slowly cooling and contracting
The Moon is not geologically frozen. Its interior has been losing heat ever since it formed, and as hot rock cools, it takes up slightly less space. The Moon’s outer shell must adjust to that gradual contraction: in places, the crust is pushed together and one slab of rock is forced up over another. This creates steep, cliff-like features called lobate scarps.
The change is tiny on a human timescale, but it is a real, ongoing reshaping of the lunar surface—not the Moon breaking apart or suddenly shrinking in a visible way.
The surface records the squeeze
Images from lunar orbit have revealed scarps across the Moon. Their shapes and locations indicate that they are produced by compression, consistent with the Moon’s interior cooling. The faults beneath them can also move, releasing energy as moonquakes. Instruments left by Apollo astronauts detected such quakes, including shallow ones associated with the Moon’s crust.
A moonquake is not simply an earthquake happening on a smaller world. The Moon lacks Earth’s active system of shifting tectonic plates, but its crust can still crack and slip under stress. With no rain, wind, or flowing water to quickly wear down the scarps, some of these signs of movement remain sharply visible.
A slow process with a lasting surface trace
The Moon’s contraction unfolds over immense spans of time, so it poses no sudden threat to observers on Earth. Its unsettling quality is more geological: even a familiar, seemingly quiet world can still change from within, and the cliffs on its surface preserve evidence of that slow pressure being released.
